Part garage conversion - wall and floor spec

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Hi - looking to convert 3/4 of an integral garage, leaving the roller shutter door in place to form a small front storage / workspace on the front of a new bedroom.

Much rather do it myself and in a way that could be reversible later on and am fine with general construction / timber-work etc but struggling to find :

1. Required spec of the partition wall - ie can it be just stud partition, obviously insulated and vapour proof if need be, but can it just rest on the existing floor slab (with DPC) or maybe have a couple of courses of bricks as a base? - provided no foundations involved.

2. Best floor method - to come up 250mm to match internal house. Total 3.16m span. Prefer suspended timber floor but I'm reading a possible need for 150mm gap beneath timbers - which looks to mean only approx 80mm floor joists - which according to online span calcs is not enough even if intermediate supports - so maybe insulation and screed is only way but thats not very reversible.

Will engage with building control prob via Building Notice etc, but would really like a head start first so any advice or pointers to other online resources appreciated - most of what I've found is not relevant to part conversion.

External walls are already full brick/block cavity and insulated, roof already insulated and existing side window in place which will be upgraded so a fair amount already covered.
 
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Hi,

For 2). You could consider a load bearing insulation block, such as Jabfloor:

Screenshot_20211106-030748_Adobe Acrobat.jpg


Where a vapour barrier and wooden board structure can sit directly on top of the insulation blocks; very easily removable :)

More info below.
 

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Hi,

For 2). You could consider a load bearing insulation block, such as Jabfloor:

Where a vapour barrier and wooden board structure can sit directly on top of the insulation blocks; very easily removable :)

More info below.

Thank you. A quick google shows various thicknesses including a 230mm thick version available, leaving 20mm for floorboards etc. Could be on to something there, cheers will look in to it further

Now just that wall !
 
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Hiya, thanks for the link. I did see that but didn't think it too relevant as my wall is planned to be a single dividing wall effectively between the new bedroom and a small 1.5m deep storage space - and I'm hoping the wall can be just of stud construction only with no brickwork involved, apart from maybe a course or two of bricks on a (foundationless) floor, which is just a thought to aid the stud construction. It will have to be well insulated and vapour / damp protected as it will be the only barrier between the bedroom and the rear of a thin metal roller door.

I'm also slightly puzzled that the sketch in that thread shows the floor timbers sat direct on the garage floor whereas I've seen references such as "A minimum gap of 150mm should be kept between the existing concrete ground and the underside of the timber.". Maybe that relates to different floor systems and whether there is already an integral DPM - which that floor has but I do not know if mine does.

Will keep digging, but thank you for the thought.
 
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So your garage floor is 230mm lower than the house, why not insulate, dpm etc, then screed to bring it to where it needs to be for your floor covering, then just build Straight off the ‘new’ surface?

If that’s not reversible enough, do as Grinch has suggested. Cut a slot in the insulation to put a base plate or couple stacked up then build your stud work.
 
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So your garage floor is 230mm lower than the house, why not insulate, dpm etc, then screed to bring it to where it needs to be for your floor covering, then just build Straight off the ‘new’ surface?

If that’s not reversible enough, do as Grinch has suggested. Cut a slot in the insulation to put a base plate or couple stacked up then build your stud work.

Hi, Just to clarify, the garage floor is 250 below - the 230 mentioned was leaving approx 20mm for floorboards.

I'm trying to stay away from screed / concrete, not only from the reversibility angle but also access is not ideal for heavier / wider wagons and even more from the point I'm trying to avoid bringing in other trades where possible, not just from a cost point of view but I'd like to DIY as much as possible. The bulk insulation does currently look the way to go, maybe not quite as cheap as timber but a hell of a lot quicker.
 
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Engineered flooring may be better than t&g if you are floating, as it will be flatter, and give a better finish. I’ve always found t&g elbowed or warped before putting it down.

Good luck.
 
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I would guess the stud wall would also need to be 30 minutes fire rated between a garage and bedroom.
 
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I would guess the stud wall would also need to be 30 minutes fire rated between a garage and bedroom.

Yup - I don't mind over spec'ing things at all, especially fire resistance - and I usually go overboard on heat and sound insulation as well - I'm a Mechanical Engineer and naturally over engineer my DIY'ing - it would take me a hundred years to build a house as I fret over straightness, mm's, strength - etc. It has been mentioned some of my previous over engineered efforts would survive a nuclear blast :(
 
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A typical stud wall betwixt say a garage and internal space could look like (from outside in) ...

X 2 two layers 12.5mm plasterboard or one layer of fireline board, tape joints and skim.

50mm Celotex across studs (foil tape joints).

100mm stud partition.

100mm Celotex between studs (foil tape joints)

18mm ply on the warm side (for fixing to).

12.5mm plasterboard, tape joints and skim.
 
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A typical stud wall betwixt say a garage and internal space could look like (from outside in) ...

X 2 two layers 12.5mm plasterboard or one layer of fireline board, tape joints and skim.

50mm Celotex across studs (foil tape joints).

100mm stud partition.

100mm Celotex between studs (foil tape joints)

18mm ply on the warm side (for fixing to).

12.5mm plasterboard, tape joints and skim.

Excellent thanks.

I'd prob do the 2 x layers 12.5 instead of the Fireline as that will help with noise - there is a road the other side of the garage door. I actually use Soundlam / Soundbloc PB wherever possible having previously built recording studios with very high sound reduction performance. The thick dense outer layer of PB and inner / warm side layers will act as a nice 2 leaf system for sound reduction. I'll check Soundlam's fire performance out.

I take it the plywood is a luxury rather than necessity? I can add it if need be though. 205mm overall thickness isn't bad I guess.

Thanks again.
 
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Correct but an absolute boon.
Right I'm ready to take the plunge and do the conversion, including the wall as per your recommended spec - but I would now like to put a door in to the new stud wall to allow access from the new bedroom to the new storeroom from inside. I'd like it to be a fairly high spec door from a noise / thermal point of view for my own benefit but are there any issues around putting this door in? I've uploaded the attached plan so you can see everything going on.

Thanks for your ongoing help.
 

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